1. Field of the Invention
This invention relates to pipe inspection apparatus of the type which is inserted into the bore of a pipe for the purpose of examining the wall of the pipe for defects, cracks or other discontinuities.
2. The Prior Art
The usual pipe inspection apparatus for examining, for example, gas pipelines comprises a vehicle, or a train of vehicles, which is propelled along the pipeline by the gas flow in the pipeline.
One favored technique for examining the walls of the pipe as the vehicle is propelled along the pipe uses ultrasonic probes. In one arrangement, ultrasonic transducers are mounted in a number of wheels which are urged into contact with the wall of the pipe. In use, ultrasound generated by the transducers is transmitted across the interface between the wheel and the wall of the pipe into the pipe wall. Ultrasound reflected or refracted from within the pipe wall is in turn received by the transducers within the wheels and subsequently analyzed. This technique requires intimate contact at all times between the wheel and the pipe wall so as to reduce or eliminate losses of the ultrasound signal at the interface between the wheel and the pipe wall.
Another important consideration is that the ultrasonic transducers, and hence the wheels, must be correctly aligned in the pipe. In one arrangement, a plurality of wheel probes are equispaced around the inner circumference of the pipe and arranged so that the wheels roll along the length of the pipe. The transducers inside the wheels are arranged to examine the pipe wall over a band which lies in a plane normal to the longitudinal axis of the pipeline. It is relatively easy to achieve a band normal to the longitudinal axis of the pipe on straight runs of the pipeline if the assembly of wheel probes are located midway along an elongated vehicle which is provided at each end with a means for locating the vehicle concentrically in the pipe. However, it becomes more difficult to ensure that the transducers are correctly aligned in the pipe and are also urged against the wall of the pipe with sufficient pressure to ensure intimate contact when the vehicle is negotiating a bend. This is because those wheel probes on the inside of the bend will tend to be forced against the pipe, whereas those on the outside of the bend will tend to be pulled away from the pipe wall.
An object of the present invention is to provide pipe inspection apparatus which will cater to bends in the pipe-line, and, in some cases, will accommodate changes in the diameter of the pipeline, without upsetting, to an unacceptable degree, the alignment, positioning and degree of contact of the wheel probes in the bore of the pipeline.